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C. E. BERRY June 3, 1958 END SUPPORT ARRANGEMENTS FOR STRING GALVANOMETER Filed Oct. 8, 1954 RECORD/N6 AMPLIFIER FIG. 2.

INVENTOR. CLIFFORD E. BERRY Mg, Mao

ATTORNEYS END SUPPORT ARRANGEMENTS FOR STRING GALVANOMETER Cliiford E. Berry, Altarlcna, Calif., assignor, by mesne assignments, to Consolidated Electrodynamics Corporation, Pasadena, Calif., a corporation of California Application October 8, 1954, Serial No. 461,087

Claims. (Cl. 324154) This invention relates to improvements in string galvanometers, and it has particular reference to arrangements for supporting the ends of the string element of such galvanometers.

When large amplitudes are required from a string galvanometer, such as when the galvanometer is employed in a direct writing oscillograph, the string element must be deflected large distances. One arrangement for achieving this result is to employ a flexible conductor as the string element, and to support it by springs at its two ends so that the central portion of the string can be deflected transversely over a large distance in either direction. Application Serial Number 461,088, which was filed on October 8, 1954, by Lewis B. Browder, discloses such a string galvanoineter arrangement.

The spring supports at the two ends of the string make it difficult to provide electrical connections to the string because the two end supports must be free to move. t is undesirable to solder the string to the springs and then provide external electrical connections to the springs because the angle through which the string must be bent as it leaves the spring results in high local stresses and rapid failure of the string element due to fatigue. Thus, it is desirable to provide a hinge connection. When this is done some provision must be made for assuring a low resistance connection to the string because electrical connection must be made to the string through the hinge connection, and variations in contact resistance at the hinge may cause erratic response.

These difiiculties are overcome in the present invention by employing leaf springs as the end supports for the string element, and a pair of pins are affixed to the ends of the respective leaf springs with the string being looped around the respective pins in a loose fit. The string extends beyond the pins at each end to provide pigtail connections for coupling the conductive string to a signal source. With such an arrangement the pigtails are subjected mainly to torsional stresses and hence have along life. The pigtails provide a reliable electrical connection to the string element because they are part of the string itself, yet they are arranged to exert negligible forces upon the tring element.

Preferably, the pole pieces which provide the magnetic field for the string element are provided with recessed or cut out areas arranged so that the length of the conductive string upon which the magnetic field operates increases as the central portion of the string is deflected in either direction, so as to compensate for variations in the tension in the string and provide a substantially linear current-deflection response. This feature of the galvanometer is covered in my application Serial Number 461,086, which was filed on October 8, 1954.

The invention is explained in more detail with reference to the drawings, in which:

Fig. 1 is an elevation view of a string galvanometer utilizing the end supports of the present invention;

Fig. 2 is a sectional view along line 22 of Fig. i;

Fig. 3 is a perspective view of one of the spring supports;

Fig. 4 shows how the string element of the galvanometer may be attached to the spring support, with a portion Patented June 3,

of the string extending beyond the spring support to provide a pigtail; and

Fig. 5 shows an alternative arrangement for attaching the string element of the galvanometer to the pin which is carried by the spring support.

The string element is a flexible conductor iii which is supported by a pair of leaf springs 12 and 14. The ends of the leaf springs are notched, and cylindrical-shaped pins 16 and 18 are affixed to the notched ends of the springs. The string element is looped around the respective pins in a loose lit, and the ends of the string element extend approximately perpendicularly with respect to the direction of movement of the strings to form a pair of pigtails NA and 103 which are connected to a pair of terminals 2t and 22 for coupling the string to a signal source, such as the recording amplifier 24. The terminals 29 and 7.2 and the springs 12 and 14 are mounted on a rigid bar 26 which is afiixed to the magnetic yoke. Each of the terminals 28, 22 is located approximately along the axis of the adjacent pin 16, 13. The springs and the terminals are insulated from the rest of the stnlcture.

Figs. 4 and 5 show two arrangements for looping the string element around the pins at the ends of the springs so as to provide suitable hinge connections between the springs and the string element.

In the arrangement of Fig. 4, the flexible conductor it) is looped around the pin 16 a full turn, with the end portion thereafter being bent around the portion of the string which is under tension and brought back upon itself for one-half turn. Then it is bent at right angles to form a pigtail connection liiA. if desired, the portion of the flexible conductor which is brought back upon it self for one-half turn may be soldered to the adjacent portion of the flexible conductor.

Fig. 5 illustrates an alternative arrangement for looping the flexible conductor around the pin support so as to provide a hinge connection. In this embodiment, the loop comprises one and one-half turns of the flexible conductor, with the portion of the loop along which the two portions of the conductor are adjacent being soldered together. The end portion of the flexible conductor extends substantially perpendicularly with respect to the plane of the loop to provide connections for coupling the string to a source of electrical current.

Each of the terminals 20, 22 is located approximately along the axis of the adjacent pin 16, 18 so that the pigtail portions 10A and 10B of the string which extend along the direction of the pins are subjected primarily to torsional stresses only and hence they have a long life. The pigtails provide a reliable electrical connection to the string because they are part of the string itself, yet they exert negligible forces upon the string element.

Preferably, the leaf springs are mounted to extend along a direction which is perpendicular to both the direction of the magnetic field and the direction along which the string extends, as shown in Figs. 1 and 2. With such an arrangement, the leaf springs provide resilient support along the direction of the string and they restrain movement of the ends of the string in all other directions. Also, fiexure of the springs does not displace the string from its central location between the two pole pieces, and hence the pressure of the string on the recording paper does not change as the string is deflected transversely.

The magnetic field for the string element is provided by a magnet 28 having one pole piece which comprises a pair of members 36 and 38, and having a yoke 3 connecting the other pole of the magnet and another pole piece comprising a pair of members 30 and 32. A conductive guide or anvil 40 is located between the members 30 and 32 of the upper pole piece, and it is provided with an edge 40A which extends perpendicularly with i to the tension in the string element.

respect to the length of the string element. A recording medium 42, such as current-sensitive paper, is passed over the edge of the conductive anvil between the anvil and the string element of the galvanometer so that the recording medium is located approximately in the plane of movement of the string. I

A source of electric current 44 has one terminal connected to the string element of the galvanometer, and it has the other terminal connected through a current-limiting resistor 46 to the conductive anvil. Thus, current flows through the current-sensitive recording paper at the intersection between the string element and the line formed by the edge of the conductive anvil. Hence, the electric current which flows between the string element and the conductive anvil causes a trace to be recorded on the current-sensitive recording paper in accordance with the movements of the string element.

Fig. 2 illustrates the deflection of the string from its central location between the two pole pieces. The deflection of the central portion of the string element is directly proportional to the magnetic field strength and to the electric current which flows through the string ele ment of the galvanometer, and it is inversely proportional The spring supports 12 and 14 are resilient along the direction along which the string extends, but the tension on the string increases as it is deflected from its central location. This increase in tension on the string element causes non-linearity in the current-deflection response of the galvanometer, and this non-linearity may be corrected by providing recessed or cut out areas of parabolic shape, such as areas 50 and 52, in the central portions of each of the pole pieces.

With such an arrangement, the length of the string upon which the magnetic field operates increases as the central portion of the string is deflected in either direction, so as to compensate for increases in the tension on the string as it is deflected.

By way of an example, the leaf springs may be made-of beryllium copper which is formed in the shape indicated in Fig. 3 and then age-hardened for two hours at 600 F., the pins at the ends of the springs may be nichrorne wire, and the string element may be composed of beryllium copper having a diameter of .0063 inch. In one embodiment of the invention, the tension on the string element was adjusted to approximately 50 grams so as to provide a resonant frequency of 200 cycles per second.

It will be apparent that the dimensions and the materials which are disclosed herein are merely illustrative and that various other arrangements may be employed if desired.

I claim:

1. In a string galvanometer having a pair of spaced leaf springs for supporting the flexible conductor element of the galvanometer, the improvement which comprises a pair of cylindrical pins affixed to the ends of the respective leaf springs with each cylindrical pin being afiixed to the side of the leaf spring which faces away from the other spring, each of the leaf springs having a notch in its end where the cylindrical pin is aflixed to it, and a flexible conductor extending through the notches and between the pins on the leaf springs so that it is under tension, the conductor being looped around the respective pins in a loose fit with the respective ends of the conductor extending beyond the pins substantially perpendicularly with respect to the direction along which its supporting leaf spring may move, and a pair of fixed terminals connected to the respective ends of said conductor, with each terminal being located approximately along the axis of the adjacent cylindrical pin so that the end portions of the conductor are subjected primarily to torsional stresses and exert negligible forces uopn the movable portion of the flexible conductor which is under tension.

2. In a string galvanometer having means for producing a magnetic field, and a pair of leaf springs located 4 at opposite ends of the magnetic field for supporting a flexible conductor element in the magnetic field, the improvement which comprises a pair of pins aflixed to the ends of the respective leaf springs, and a flexible conductor extending between and supported under tension by the pins on the leaf springs, the flexible conductor being looped around the respective pins in a loose fit, with each of the loops in the flexible conductor comprising one and one-half turns of the conductor, with the portion of the loop along which two portions of the conductor are ad jacent being affixecl together and with each of the end portions of the flexible conductor extending substantially perpendicularly with respect to the plane of the adjacent loop to provide connections for coupling the flexible conductor to a source of electric current.

3. in a string galvanometer having means for producing a magnetic field, and a pair of leaf springs located at'opposite ends of the magnetic field for supporting a flexible conductor element in the magnetic field, the improvement which comprises a pair of pins afiixed to the ends of the respective leaf springs, and a flexible conductor extending between and supported under tension by the pins on the leaf springs, the flexible conductor being looped around the respective pins in a loose fit, with each of the loops in the flexible conductor comprising a full turn of the conductor with the end portion thereafter being bent around the portion of the conductor which is under tension and brought back upon itself for one-half turn, and then extending beyond the pin to provide electrical connections for coupling the flexible conductor to a source of electric current.

4. In a string galvanometer having a string element designed to undergo lateral deflection substantially in one plane, the improvement which comprises a pair of cantilever leaf springs supported in spaced relationship at their fixed ends by the galvanometer for supporting the string element between them, each of 'the springs extending approximately in the direction transverse to the length of the string, pins aflixed to the free ends of the springs, and

the string element being bent into a loop at each end around the pin in a loose fit so as to form a hinge connection at each end of the string element to a corresponding spring, the plane of each loop being oriented approximately in the direction of lateral movement of the element so as to prevent high local stresses from being set up in the string element.

5. In a string galvanometer having a string element designed to undergo lateral deflections substantially in one plane, the improvement which comprises a pair of spaced leaf springs coupled to the galvanometer for supporting the string element between them, and means for making a hinge connection between each end of the string and the corresponding spring, with the hinge connections adapted to swing alon the direction of vibration of the string element so as to prevent high local stresses from being set up in the string element, the string element extending past the hinge connection at each end in a direction approximately perpendicular to the plane of vibration of the string element so that the electrical connection may be made directly to the end of the string element and so that the ends of the string element tend to exert mere torsional opposition to the lateral deflection of the string element.

References Cited in the file of this patent UNITED STATES PATENTS 2,065,907 Perreault Dec. 29, 1936 2,169,476 Gill Aug. 15, 1939 2,539,158 Parsegian Jan. 23, 1951 2,563,167 Hathaway Aug. 7, 1951 2,678,424 Heiland May 11, 1954 FOREIGN PATENTS 1,024,742 France Apr. ,7, 1953 

